finally getting accurate answers

.gitignore

@@ -28,3 +28,6 @@ frontend/dist/
 *.log
 .DS_Store
 Thumbs.db
+
+--- Local data dumps (KB replicas, pg_dumps) — never committed ---
+data/

app/rag/agent.py

@@ -66,6 +66,16 @@ task 04):
    each line truncated to 200 chars. A grep is a **locator**, not a
    context-adder: it never appends to the answer context (only
    ``read`` does — ``holder.read_docs`` is untouched by a grep).
+   The 2026-09-05 incident teaching (the harness prior is that grep
+   takes a REGEX; this grep is a fixed substring and the contract does
+   not change): when a grep RAN but found nothing and the pattern is
+   regex-shaped (:func:`looks_like_regex`) with a non-empty
+   :func:`plain_form`, the no-match result is the TEACHING line —
+   :data:`NO_MATCHES_REGEX` / :data:`NO_MATCHES_REGEX_SCOPED` — which
+   states the plain-substring contract and hands over the plain-form
+   retry hint; a grep that matched, or a no-match for a plain pattern
+   (or one that reduces to nothing), is byte-identical to the ordinary
+   line. Still a (counted) result, never a refusal.
 3. Rejected calls get a one-line refusal and count in nothing
    (``holder.tool_calls`` tracks executed calls only): unknown tool name
    → ``"Unknown tool."``; a ``read`` without a usable ``path`` (missing,
@@ -163,6 +173,7 @@ from __future__ import annotations
 
 import json
 import logging
+import re
 from collections.abc import AsyncIterator, Sequence
 from dataclasses import dataclass, field
 from typing import Any, cast
@@ -268,12 +279,16 @@ AGENT_TOOLS: list[dict[str, Any]] = [
                 "Search the indexed documents for an exact string "
                 "(case-insensitive) and return up to 20 matching lines "
                 "as `source/path:line: text` — a locator, not a "
-                "context-adder: read the winner with `read`. For a "
+                "context-adder: read the winner with `read`. The "
-                "normal search pass ONLY `pattern` — it searches every "
+                "pattern is a plain substring, NEVER a regex — if a "
-                "document and that is how you search the knowledge "
+                "pattern with regex syntax (like '.*' or '\\.') comes "
-                "base; never pass a source name as `path` (a source "
+                "back with no matches, retry with the plain text you "
-                "name is not a document). Call one tool at a time — "
+                "expect to see. For a normal search pass ONLY `pattern` "
-                "wait for this result before your next call."
+                "— it searches every document and that is how you "
+                "search the knowledge base; never pass a source name "
+                "as `path` (a source name is not a document). Call one "
+                "tool at a time — wait for this result before your "
+                "next call."
             ),
             "parameters": {
                 "type": "object",
@@ -282,7 +297,8 @@ AGENT_TOOLS: list[dict[str, Any]] = [
                         "type": "string",
                         "description": (
                             "The exact text to search for (a plain "
-                            "substring, not a regex)"
+                            "substring, not a regex — no '.*', no "
+                            "'\\.', no character classes)"
                         ),
                     },
                     "path": {
@@ -417,6 +433,79 @@ SEARCH_LINE_LIMIT = 200
 NO_MATCHES = "No matches for '{pattern}' in the knowledge base."
 NO_MATCHES_SCOPED = "No matches for '{pattern}' in {source}/{path}."
 
+#: Teaching no-match lines (the 2026-09-05 incident — owner chat:
+#: "Qwen 3.8" question failed repeatedly). The harness-trained prior is
+#: that ``grep(pattern)`` takes a REGEX (pi.dev's grep, ripgrep, grep
+#: itself); this app's grep is a case-insensitive FIXED SUBSTRING
+#: (owner-locked A5 — the contract does not change). A regex-shaped
+#: pattern (``qwen.*3\.8``, ``qwen 3\.8``) can therefore never match, and
+#: the bare no-match line above made the turbo model trust the miss and
+#: end the turn with a wrong "I searched the entire knowledge base"
+#: refusal. These lines are the deterministic teaching: the same result
+#: (a no-match is still a *result* — counted, no context added) with the
+#: correct contract stated and a plain-text retry hint (the
+#: :func:`plain_form` of the pattern, when non-empty). Deterministic only
+#: (owner permission 2026-09-03: "deterministic guardrails only right
+#: now"): no model participates in detection or repair.
+NO_MATCHES_REGEX = (
+    "No matches for '{pattern}'. grep matches a plain substring "
+    "(case-insensitive), not a regex — '.*', '\\.' and the like are "
+    "literal text here, so that pattern can never match. Retry with the "
+    "plain text you expect to see (e.g. '{plain}')."
+)
+NO_MATCHES_REGEX_SCOPED = (
+    "No matches for '{pattern}' in {source}/{path}. grep matches a plain "
+    "substring (case-insensitive), not a regex — retry with the plain "
+    "text you expect to see (e.g. '{plain}')."
+)
+
+#: One of these metacharacters anywhere in the pattern marks it
+#: regex-shaped (the detection for the teaching no-match lines above).
+#: Plain substrings that happen to contain one ("C++", "a|b") are
+#: affected only on a NO-MATCH — a pattern that matched literally still
+#: gets its ordinary result, so the teaching can never suppress a real
+#: hit.
+_REGEX_META_RE = re.compile(r"[*+?(){}\[\]|\\^$]")
+
+
+# Backslash + a non-alphanumeric char is an escaped literal (``\\.`` →
+# ``.``); backslash + an alphanumeric is a class shorthand (``\\d``,
+# ``\\w``, ``\\s``) with no plain-text equivalent (→ dropped).
+_ESCAPE_RE = re.compile(r"\\(.)")
+
+
+def looks_like_regex(pattern: str) -> bool:
+    """True when *pattern* carries regex metacharacters (see
+    :data:`_REGEX_META_RE`). Pure detection — the grep itself stays a
+    fixed substring (owner-locked A5)."""
+    return _REGEX_META_RE.search(pattern) is not None
+
+
+def plain_form(pattern: str) -> str:
+    """A deterministic plain-text retry hint for a regex-shaped pattern.
+
+    The hint is the pattern reduced to literal text, in this order:
+    drop ``.*`` runs on the RAW pattern first (the wildcard — an escaped
+    ``\\.`` + ``\\*`` pair carries no raw ``.*`` run, so a literal dot
+    survives), unescape (``\\.`` → ``.``; class shorthands like ``\\d``
+    dropped), keep only the FIRST ``|`` alternative, drop character
+    classes (``[0-9]``), drop quantifier runs (``*``, ``+``, ``?``,
+    ``{2,3}``), drop group parens and anchors (contents kept). Whitespace
+    is preserved. ``qwen.*3\\.8`` → ``qwen3.8`` (the incident's exact
+    recovery), ``llama\\.cpp`` → ``llama.cpp``, ``qwen[0-9]+`` →
+    ``qwen``. A pattern made of pure metacharacters reduces to ``""`` —
+    callers then fall back to the ordinary no-match line (no hint).
+    """
+    p = re.sub(r"\.\*", "", pattern)  # .* wildcard runs (raw form)
+    p = _ESCAPE_RE.sub(lambda m: m.group(1) if not m.group(1).isalnum() else "", p)
+    p = p.split("|", 1)[0]  # first alternative only — a hint, not an answer
+    p = re.sub(r"\[[^\]]*\]", "", p)  # character classes carry no literal text
+    p = re.sub(r"\{[^{}]*\}", "", p)  # {n} / {n,} / {n,m} quantifiers
+    p = re.sub(r"[*+?]+", "", p)  # stray * + ? quantifiers
+    p = p.replace("(", "").replace(")", "")
+    p = p.replace("^", "").replace("$", "")
+    return p.strip()
+
 
 def list_catalog(db: Session) -> list[tuple[str, str, str]]:
     """Every indexed document as ``(source, path, title)``.
@@ -694,6 +783,24 @@ def _execute_tool(
         # Locked A5: a grep never adds context — read_docs untouched.
         if not matches:
             shown = pattern[:100]  # keep a long pattern short in the line
+            # The 2026-09-05 incident teaching: a regex-shaped pattern
+            # (the harness prior) can NEVER match a fixed-substring
+            # grep, so a no-match for one is not "the KB lacks this" —
+            # it is "the pattern was in the wrong form". Teach the
+            # contract and hand over the plain-form retry hint (when the
+            # reduction is non-empty); a plain pattern (or a pattern
+            # that reduces to nothing) keeps the ordinary line
+            # byte-identical.
+            plain = plain_form(pattern) if looks_like_regex(pattern) else ""
+            if plain:
+                if scoped_to is not None:
+                    return NO_MATCHES_REGEX_SCOPED.format(
+                        pattern=shown,
+                        source=scoped_to[0],
+                        path=scoped_to[1],
+                        plain=plain[:100],
+                    )
+                return NO_MATCHES_REGEX.format(pattern=shown, plain=plain[:100])
             if scoped_to is not None:
                 # The scoped no-match line is keyed on the resolved
                 # source/path (== the argument, stripped).

app/rag/prompts.py

@@ -149,8 +149,11 @@ TOOLS_SECTION: str = (
     "path (without the source name) will not resolve. `grep` locates an "
     "exact string (case-insensitive) in the indexed documents and "
     "returns up to 20 matching `source/path:line: text` lines — a "
-    "locator, not a context-adder: read the winner with `read`; for a "
+    "locator, not a context-adder: read the winner with `read`. A grep "
-    "normal search pass only `pattern` — its optional `path` argument "
+    "pattern is a plain substring, NEVER a regex — '.*' and '\\.' are "
+    "literal text there; if such a pattern returns no matches, retry "
+    "with the plain text you expect to see. For a normal search pass "
+    "only `pattern` — its optional `path` argument "
     "limits the search to one document you already know, by the same "
     "combined `source/path` string; never a source name — a bare "
     "document path (without the source name) will not resolve there "

app/rag/retriever.py

@@ -3,8 +3,27 @@
 * **Vector list** — top-N chunks by cosine distance (``embedding <=> $1``),
   each carrying its cosine ``1 − distance`` (the honesty-gate input).
 * **Lexical list** — top-N chunks matching an OR-``tsquery`` over the
-  question's tokens, ordered by ``ts_rank``. This is what finds
+  question's tokens, ordered by ``ts_rank``, UNION the name-hit list:
-  name-your-tool questions ("gitlab") that vector similarity buries.
+  documents whose normalized name (title + path stem, alnum-only,
+  lowercased) contains a DIGIT-BEARING normalized question token of
+  length >= 4 — bare tokens (``1panel``) and the join of adjacent
+  question tokens starting with a letter ("Qwen 3.8" → ``qwen38``).
+  The digit requirement is the precision guard: plain prose words
+  ("server", "arguments" — 4+ chars but no digit) never name-match,
+  while versioned product names (the incident's whole point) always
+  carry one. The name-hit documents LEAD the lexical list (ranked by
+  match count, then total matched length, then catalog order; capped
+  at :data:`NAME_HIT_LIMIT`),
+  the FTS rows follow. This is what finds name-your-tool questions
+  ("gitlab") that vector similarity buries — and, the 2026-09-05
+  incident, the versioned-name case the default parser lexes
+  incompatibly (question "Qwen 3.8" → ``qwen``/``3``/``8`` can never
+  match a document's ``qwen3``/``8``/``27b`` tokens, while every
+  unrelated llama.cpp quadlet out-ranks the target on the shared
+  ``llama``/``cpp`` tokens). The name-hit rows carry ``fts_hit=True``
+  (they ARE the lexical signal — the A8 honesty gate then answers
+  instead of deflecting) and ``cosine=0.0``; the RRF fusion is
+  unchanged (same lists, same ``1/(k+rank)`` terms).
 * **Fusion** — Reciprocal Rank Fusion (``score = Σ 1/(k + rank)`` over the
   lists a chunk appears in; chunks hit by both lists get both terms). The
   fused score ranks; :meth:`select_documents` and :func:`weak_hit_titles`
@@ -26,6 +45,7 @@ import re
 import uuid
 from collections.abc import Sequence
 from dataclasses import dataclass, replace
+from pathlib import Path
 
 from sqlalchemy import select, text
 from sqlalchemy.orm import Session
@@ -38,8 +58,78 @@ from app.models import Chunk, Document
 #: path never truncates (A7 revised, owner permission 2026-08-24).
 TRUNCATION_MARKER = "[…truncated…]"
 
-#: Alphanumeric tokens of a question (``to_tsquery`` input, OR-joined).
+#: Alphanumeric tokens of a question (``to_tsquery`` input, OR-joined),
-_TOKEN_RE = re.compile(r"[a-z0-9]+")
+#: with DOTTED tokens kept whole (``llama.cpp`` → ``llama.cpp``). The
+#: default parser lexes a dotted word as ONE lexeme (``to_tsvector`` of
+#: "llama.cpp" → ``'llama.cpp'``; of "Qwen 3.8" → ``'3.8'``), so a split
+#: token (``llama`` | ``cpp``) can never match the document side — the
+#: 2026-09-05 incident's question phrase "llama.cpp" lexed
+#: incompatibly on both sides of the query. Dotted tokens are passed
+#: through as single ``to_tsquery`` lexemes (verified: Postgres accepts
+#: ``'llama.cpp'`` and ``'3.8'`` as lexemes).
+_TOKEN_RE = re.compile(r"[a-z0-9]+(?:\.[a-z0-9]+)*")
+
+#: Name-hit policy (the 2026-09-05 incident): a question token shorter
+#: than this (normalized) is too weak a name signal ("3", "8", "the") —
+#: it would match half the KB by accident.
+NAME_TOKEN_MIN_LEN = 4
+
+#: The name-hit list may contribute at most this many documents to the
+#: lexical side (before the FTS rows); the rest are dropped.
+NAME_HIT_LIMIT = 10
+
+#: Alphanumeric runs of a lowercased string (name normalization).
+_ALNUM_RE = re.compile(r"[a-z0-9]+")
+
+
+def _normalize_name(s: str) -> str:
+    """Lowercased, alnum-only form of *s* (``Qwen 3.8`` → ``qwen38``)."""
+    return "".join(_ALNUM_RE.findall(s.lower()))
+
+
+def name_hit_tokens(question: str) -> list[str]:
+    """The normalized name-match candidates of one question.
+
+    Only DIGIT-BEARING candidates count (the precision guard — a plain
+    prose word like "server" or "arguments" must never name-match a
+    document; a versioned product name always carries a digit):
+
+    * the :func:`_normalize_name` form of every whitespace token, kept
+      when at least :data:`NAME_TOKEN_MIN_LEN` chars (``1panel``,
+      ``qwen38`` from a single written token);
+    * the versioned-name JOIN — the normalized concatenation of every
+      ADJACENT token pair whose SECOND token is purely numeric (a
+      version number: ``"… for Qwen 3.8"`` → ``Qwen`` + ``3.8`` joins
+      to ``qwen38``; prose joins like ``correct`` + ``llama`` and the
+      word-after-version boundaries like ``3.8`` + ``show`` are
+      dropped). A purely-numeric second token means the join always
+      starts with the first token's text (a letter in practice), so no
+      digit-leading artifact (``38show``) can survive.
+
+    Order of first appearance, de-duplicated.
+    """
+    tokens = question.split()
+    out: list[str] = []
+    seen: set[str] = set()
+
+    def add(tok: str) -> None:
+        if (
+            len(tok) >= NAME_TOKEN_MIN_LEN
+            and any(ch.isdigit() for ch in tok)
+            and tok not in seen
+        ):
+            seen.add(tok)
+            out.append(tok)
+
+    for i, raw in enumerate(tokens):
+        norm = _normalize_name(raw)
+        add(norm)
+        if i + 1 < len(tokens):
+            next_norm = _normalize_name(tokens[i + 1])
+            if next_norm and next_norm.isdigit():
+                add(norm + next_norm)  # the versioned-name join
+    return out
+
 
 #: One row of the lexical candidate query (all fields needed to build a
 #: detached :class:`Document` plus the chunk fields and ``ts_rank``).
@@ -96,11 +186,14 @@ class RetrievedChunk:
 def lexical_tsquery(question: str) -> str | None:
     """OR-joined token string for ``to_tsquery('english', …)``, or ``None``.
 
-    Tokens are lowercased ``[a-z0-9]+`` runs, de-duplicated in order of
+    Tokens are lowercased ``[a-z0-9]+`` runs with DOTTED words kept whole
-    first appearance. Postgres does the lexing/stemming; a question whose
+    (see :data:`_TOKEN_RE` — the default parser lexes ``llama.cpp`` as
-    tokens are all stopwords lexes to an *empty* tsquery (which matches
+    one lexeme, so the query must carry it whole too), de-duplicated in
-    nothing), so no special-casing is needed there. Pure-symbol questions
+    order of first appearance. Postgres does the lexing/stemming; a
-    ("???", "🔧") yield no tokens → ``None`` → no lexical query at all.
+    question whose tokens are all stopwords lexes to an *empty* tsquery
+    (which matches nothing), so no special-casing is needed there.
+    Pure-symbol questions ("???", "🔧") yield no tokens → ``None`` → no
+    lexical query at all.
     """
     seen: set[str] = set()
     tokens: list[str] = []
@@ -181,21 +274,141 @@ def _vector_candidates(
     ]
 
 
-def _lexical_candidates(db: Session, question: str, limit: int) -> list[RetrievedChunk]:
+#: One name-hit row: the document fields (detached :class:`Document`)
-    """Top-*limit* chunks matching the question's OR-tsquery (A7).
+#: plus the representative chunk — the ``is_summary`` chunk when the
-
+#: document has one (its natural-language summary is the best chunk of
-    Ordered by ``ts_rank`` (with ``d.path, c.position`` as the
+#: a machine file, and the chunk the vector list is likeliest to have
-    deterministic tie-break); an empty tsquery (stopword-only question)
+#: ranked too, so the RRF merge dedupes cleanly), else chunk 0.
-    simply matches nothing.
+_NAME_HIT_SQL = text(
     """
+    SELECT d.id            AS doc_id,
+           d.source        AS source,
+           d.path          AS path,
+           d.full_path     AS full_path,
+           d.title         AS title,
+           d.content       AS doc_content,
+           d.content_hash  AS content_hash,
+           d.indexed_at    AS indexed_at,
+           c.id            AS chunk_id,
+           c.position      AS position,
+           c.content       AS content,
+           c.is_summary    AS is_summary
+    FROM documents d
+    LEFT JOIN LATERAL (
+        SELECT id, position, content, is_summary
+        FROM chunks
+        WHERE document_id = d.id
+        ORDER BY is_summary DESC, position ASC
+        LIMIT 1
+    ) c ON true
+    WHERE d.id = ANY(:ids) AND c.id IS NOT NULL
+    """
+)
+
+
+def _name_hit_chunks(db: Session, question: str) -> list[RetrievedChunk]:
+    """The documents whose NAME matches the question (the 2026-09-05
+    incident, the versioned-name signal).
+
+    A document is a name hit when its normalized name —
+    :func:`_normalize_name` of its ``title`` followed by the normalized
+    path stem (``qwen3.8-27b-juggernaut-vulkan.container`` →
+    ``qwen3827bjuggernautvulkan``) — contains at least one
+    :func:`name_hit_tokens` candidate (``qwen38``). Ranked by
+    (distinct matched tokens, total matched length, source, path) —
+    catalog order is the final deterministic tie-break — capped at
+    :data:`NAME_HIT_LIMIT`. Each hit becomes one lexical
+    :class:`RetrievedChunk` (its representative chunk, ``fts_hit=True``,
+    ``cosine=0.0``). Two lightweight queries: one projection over
+    (id, source, path, title) in catalog order, one LATERAL chunk
+    fetch for the ≤ :data:`NAME_HIT_LIMIT` winners (no full-content
+    load; the content joins in via the row fetch below).
+    """
+    tokens = name_hit_tokens(question)
+    if not tokens:
+        return []
+    rows = db.execute(
+        select(Document.id, Document.source, Document.path, Document.title).order_by(
+            Document.source, Document.path
+        )
+    ).all()
+    scored: list[tuple[int, int, uuid.UUID]] = []
+    by_id: dict[uuid.UUID, tuple[str, str]] = {}  # id -> (source, path)
+    for doc_id, source, path, title in rows:
+        by_id[doc_id] = (source, path)
+        name = _normalize_name(title) + _normalize_name(Path(path).stem)
+        matched = [t for t in tokens if t in name]
+        if matched:
+            scored.append((len(matched), sum(len(t) for t in matched), doc_id))
+    if not scored:
+        return []
+    # Ranked by (distinct matched tokens, total matched length), the
+    # deterministic catalog tie-break (source, path) last.
+    scored.sort(
+        key=lambda s: (-s[0], -s[1], by_id[s[2]][0], by_id[s[2]][1])
+    )
+    ids = [s[2] for s in scored[:NAME_HIT_LIMIT]]
+    hit_rows = list(db.execute(_NAME_HIT_SQL, {"ids": ids}).all())
+    # The LATERAL query returns winners in id order; re-order by the
+    # ranked order computed above so the lexical list is deterministic.
+    order = {doc_id: rank for rank, doc_id in enumerate(ids)}
+    hit_rows.sort(key=lambda row: order[row.doc_id])
+    out: list[RetrievedChunk] = []
+    for row in hit_rows:
+        doc = Document(
+            id=row.doc_id,
+            source=row.source,
+            path=row.path,
+            full_path=row.full_path,
+            title=row.title,
+            content=row.doc_content,
+            content_hash=row.content_hash,
+            indexed_at=row.indexed_at,
+        )
+        out.append(
+            RetrievedChunk(
+                chunk_id=row.chunk_id,
+                position=row.position,
+                content=row.content,
+                score=0.0,  # filled in by :func:`fuse`
+                document=doc,
+                cosine=0.0,  # no vector rank — name-only hit
+                fts_hit=True,  # the lexical signal — the A8 gate answers
+                is_summary=bool(row.is_summary),
+            )
+        )
+    return out
+
+
+def _lexical_candidates(db: Session, question: str, limit: int) -> list[RetrievedChunk]:
+    """The lexical candidate list: name hits, then FTS rows (A7).
+
+    The name-hit documents (:func:`_name_hit_chunks`, the versioned-name
+    signal) LEAD the list — they are the strongest lexical evidence for
+    a name-your-thing question — followed by the top-*limit* chunks
+    matching the question's OR-tsquery, ordered by ``ts_rank`` (with
+    ``d.path, c.position`` as the deterministic tie-break). Deduped by
+    chunk id (a name-hit representative chunk the FTS list also ranked
+    appears once). An empty tsquery (stopword-only question) simply
+    contributes no FTS rows; a question with no name tokens contributes
+    no name hits — both halves are independent.
+    """
+    out: list[RetrievedChunk] = []
+    seen: set[uuid.UUID] = set()
+    for rc in _name_hit_chunks(db, question):
+        if rc.chunk_id not in seen:
+            seen.add(rc.chunk_id)
+            out.append(rc)
     tsquery = lexical_tsquery(question)
     if tsquery is None:
-        return []
+        return out
     rows = db.execute(
         _LEXICAL_SQL, {"tsquery": tsquery, "limit": limit}
     ).all()
-    out: list[RetrievedChunk] = []
     for row in rows:
+        if row.chunk_id in seen:
+            continue
+        seen.add(row.chunk_id)
         doc = Document(
             id=row.doc_id,
             source=row.source,

tests/e2e/mock_llm.py

@@ -183,6 +183,40 @@ Implements just enough of the aipi surface:
     phrases are disjoint substrings — the phase-71 ordering
     convention); no existing E2E question or fixture file contains the
     phrase, so every other suite is unaffected.
+  - user message containing ``what are the correct llama.cpp
+    arguments`` (``GREP_TEACH_TRIGGER``, the 2026-09-05 incident —
+    the harness prior is that grep takes a REGEX; this app's grep is a
+    case-insensitive fixed substring, owner-locked A5) **and** the
+    system prompt carries the ``<tools>`` section -> the deterministic
+    GREP-REGEX-TEACHING flow, discriminated statelessly from the
+    messages (streaming only):
+      * request 1 (``tools`` offered, no ``tool``-role result yet):
+        stream ONLY ``tool_calls`` deltas — ``grep`` with
+        ``{"pattern": GREP_TEACH_PATTERN}`` (``qwen.*3\\.8``, id
+        ``call_0``) — the incident's regex-shaped first grep, which a
+        fixed-substring grep can NEVER match;
+      * request 2 (the last tool result is the server's TEACHING
+        no-match line — it carries ``GREP_TEACH_MARKER``):
+        ``grep`` with the plain form ``GREP_TEACH_PLAIN``
+        (``qwen3.8``, id ``call_1``) — the one-round correction;
+      * request 3 (the last tool result carries
+        ``source/path:line: text`` match lines): ``read`` the FIRST
+        match line's document by its combined ``source/path`` (id
+        ``call_2``);
+      * request 4 (the last tool result is a read result, the
+        ``"Document <combined>:\n<content>"`` shape): the
+        deterministic echo answer ``Read <combined>. <first 80
+        chars>``, ``finish_reason: "stop"`` — the loop ended in ONE
+        correction, not at the round cap.
+      * A PLAIN no-match as the last result (no match line, no
+        teaching marker — e.g. the plain pattern genuinely absent) is
+        the deterministic terminal answer ``No matches — the knowledge
+        base has no such text.`` (the flow cannot loop on a
+        well-formed pattern).
+    Checked BEFORE the SEARCH / TOOLS_TRIGGER flows (disjoint trigger
+    phrases — the phase-72 ordering convention); no existing E2E
+    question or fixture file contains the phrase, so every other suite
+    is unaffected.
   - user message containing ``show me a table`` (phase 44, markdown
     tables, TODO.md L6) -> the fixed table answer (``TABLE_ANSWER``):
     a 3-column service table, an ``<img onerror>`` XSS probe line, and
@@ -483,6 +517,34 @@ assert _CORRECTION_MARKER in CORRECTION_INSTRUCTION, (
 #: file contains the phrase, so every other suite is unaffected.
 LS_TEACH_TRIGGER = "list the files in this directory"
 
+#: The deterministic GREP-REGEX-TEACH flow (the 2026-09-05 "Qwen 3.8"
+#: incident — the harness prior is that grep takes a REGEX; this app's
+#: grep is a case-insensitive fixed substring, owner-locked A5, so a
+#: regex-shaped pattern can NEVER match, and the bare no-match line
+#: made the turbo model trust the miss and end the turn with a wrong
+#: "I searched the entire knowledge base" refusal). The flow pins the
+#: self-correction on the SSE wire: the regex-shaped first grep → the
+#: server's TEACHING no-match line (``GREP_TEACH_MARKER``) → the
+#: plain-form retry grep → the match → the read → the deterministic
+#: echo answer. Checked BEFORE the SEARCH / TOOLS_TRIGGER flows
+#: (disjoint trigger phrases — the phase-71/72 ordering convention);
+#: verified: no existing E2E question or fixture file contains the
+#: phrase, so every other suite is unaffected.
+GREP_TEACH_TRIGGER = "what are the correct llama.cpp arguments"
+
+#: The incident's regex-shaped first grep (it can never match a
+#: fixed-substring grep — that is the point of the flow).
+GREP_TEACH_PATTERN = "qwen.*3\\.8"
+
+#: The plain-form retry — the server's teaching line hands over exactly
+#: this hint (``app.rag.agent.plain_form(GREP_TEACH_PATTERN)``).
+GREP_TEACH_PLAIN = "qwen3.8"
+
+#: The marker of the agent's teaching no-match line (app.rag.agent
+#: ``NO_MATCHES_REGEX`` / ``NO_MATCHES_REGEX_SCOPED``) — the mock's
+#: plain step keys on it (a plain no-match line carries it not).
+GREP_TEACH_MARKER = "grep matches a plain substring"
+
 #: The agent's ``ls`` listing header (app.rag.agent ``_execute_tool``):
 #: ``"N documents:"`` — the first line of every catalog tool result.
 _CATALOG_HEADER_RE = re.compile(r"^\d+ documents:")
@@ -836,6 +898,61 @@ def _ls_teach_flow(body: dict[str, Any]) -> tuple[str, ...] | None:
     return ("misuse",)
 
 
+def _grep_teach_flow(body: dict[str, Any]) -> tuple[str, ...] | None:
+    """Classify a GREP-TEACH request (the 2026-09-05 incident — see the
+    ``GREP_TEACH_*`` constants). Stateless over the messages, like the
+    other marker flows:
+
+    * ``("regex",)`` — ``tools`` are offered and no ``tool``-role result
+      is in the messages yet: the incident's regex-shaped first grep —
+      ``grep`` with ``{"pattern": GREP_TEACH_PATTERN}`` (id ``call_0``).
+    * ``("plain",)`` — the LAST tool result is the server's TEACHING
+      no-match line (it carries ``GREP_TEACH_MARKER``): the one-round
+      correction — ``grep`` with the plain form (id ``call_1``).
+    * ``("read", combined, "call_2")`` — the last tool result carries
+      ``source/path:line: text`` match lines: ``read`` the FIRST match
+      line's document by its combined ``source/path`` identity.
+    * ``("answer", combined, content)`` — the last tool result is a
+      read result (``"Document <combined>:\n<content>"``): the
+      deterministic echo answer ``Read <combined>. <first 80 chars>``.
+    * ``("nomatch",)`` — the last tool result is a PLAIN no-match (no
+      match line, no teaching marker): the deterministic terminal
+      ``No matches — the knowledge base has no such text.`` answer.
+    * ``None`` — not the flow: the trigger is absent, the ``<tools>``
+      section is missing (deflected turns never carry it), or ``tools``
+      are not offered and no tool results are in the messages yet (e.g.
+      ``agent_max_rounds=0``).
+    """
+    user = _user(body).lower()
+    if GREP_TEACH_TRIGGER not in user:
+        return None
+    if "<tools>" not in _system(body):
+        return None
+    results = [
+        str(m.get("content") or "")
+        for m in _messages(body)
+        if m.get("role") == "tool"
+    ]
+    if not results:
+        if not body.get("tools"):
+            return None
+        return ("regex",)
+    last = results[-1]
+    if last.startswith(_READ_RESULT_PREFIX):
+        head, _, content = last.partition("\n")
+        # The read result is ``"Document <combined>:\n<content>"`` — the
+        # head carries the server's appended ``:`` (removed here; a
+        # document path never legitimately ends with one).
+        return ("answer", head[len(_READ_RESULT_PREFIX):].removesuffix(":"), content)
+    if GREP_TEACH_MARKER in last:
+        return ("plain",)
+    for line in last.splitlines():
+        m = _SEARCH_LINE_RE.match(line)
+        if m:
+            return ("read", m.group("sp"), "call_2")
+    return ("nomatch",)
+
+
 def long_answer() -> str:
     """~900-word deterministic walkthrough (phase 11): numbered steps plus
     a unique final line that must survive the stream untruncated."""
@@ -1307,6 +1424,50 @@ def chat_completions(body: dict[str, Any]) -> Any:
                 media_type="text/event-stream",
                 headers={"Cache-Control": "no-cache", "X-Accel-Buffering": "no"},
             )
+        # 2026-09-05 (the "Qwen 3.8" incident — the grep regex prior):
+        # the deterministic GREP-TEACH self-correction flow — checked
+        # BEFORE the SEARCH / TOOLS_TRIGGER flows (disjoint trigger
+        # phrases — the phase-72 ordering convention; the trigger needs
+        # the ``<tools>`` section, so deflected turns never hit it).
+        grep_teach = _grep_teach_flow(body)
+        if grep_teach is not None:
+            if grep_teach[0] == "regex":
+                # The incident's misuse, deterministic: the regex-shaped
+                # pattern (it can never match a fixed-substring grep).
+                stream = _tool_call_stream(
+                    "grep", {"pattern": GREP_TEACH_PATTERN}, "call_0"
+                )
+            elif grep_teach[0] == "plain":
+                # The one-round correction: the plain-form retry (the
+                # teaching line handed over exactly this hint).
+                stream = _tool_call_stream(
+                    "grep", {"pattern": GREP_TEACH_PLAIN}, "call_1"
+                )
+            elif grep_teach[0] == "read":
+                stream = _tool_call_stream(
+                    "read", {"path": grep_teach[1]}, grep_teach[2]
+                )
+            elif grep_teach[0] == "nomatch":
+                stream = _sse_stream(
+                    _apply_max_tokens(
+                        "No matches — the knowledge base has no such text.",
+                        body.get("max_tokens"),
+                    ),
+                    0.0,
+                )
+            else:  # "answer" — quote the read document (first 80 chars)
+                stream = _sse_stream(
+                    _apply_max_tokens(
+                        f"Read {grep_teach[1]}. {grep_teach[2][:80]}",
+                        body.get("max_tokens"),
+                    ),
+                    0.0,
+                )
+            return StreamingResponse(
+                stream,
+                media_type="text/event-stream",
+                headers={"Cache-Control": "no-cache", "X-Accel-Buffering": "no"},
+            )
         # Phase 68 (search tool): the deterministic search marker flow —
         # checked BEFORE the phase-37 tool flow (the more specific
         # trigger phrase wins, same convention as THINK_PARAS_TRIGGER).

tests/e2e/test_grep_regex_teaching.py

@@ -0,0 +1,485 @@
+"""The 2026-09-05 incident E2E (Playwright, mock-only): the
+grep-regex-teaching self-correction loop through the real UI.
+
+Context: the sample question "What are the correct llama.cpp arguments
+for Qwen 3.8?" failed repeatedly against the live KB. The harness
+prior is that ``grep(pattern)`` takes a REGEX (pi.dev's grep, ripgrep,
+grep itself); this app's grep is a case-insensitive fixed substring
+(owner-locked A5 — the contract does not change). A regex-shaped
+first grep (``qwen.*3\\.8``) can therefore NEVER match, and the bare
+"no matches" result made the turbo model trust the miss and end the
+turn with a wrong "I searched the entire knowledge base" refusal.
+The fix under test (``app.rag.agent``): a no-match for a regex-shaped
+pattern is the TEACHING line (``NO_MATCHES_REGEX`` /
+``NO_MATCHES_REGEX_SCOPED``) — the plain-substring contract stated,
+the ``plain_form`` retry hint handed over — so the model self-corrects
+in one round.
+
+Run in isolation (DB must be up: ``podman compose up -d db``):
+
+    uv run pytest tests/e2e/test_grep_regex_teaching.py -v --no-cov
+
+MOCK-ONLY suite: ``E2E_REAL_LLM=1`` is not supported — the gate is the
+deterministic GREP-TEACH flow in ``tests/e2e/mock_llm.py``
+(``GREP_TEACH_TRIGGER`` — "what are the correct llama.cpp arguments"
+— + the HIGH prompt's ``<tools>`` section): the incident's regex-
+shaped first grep (``grep`` with ``{"pattern": "qwen.*3\\.8"}``, id
+``call_0``) → the agent's TEACHING no-match line (the mock's plain
+step keys on the marker ``grep matches a plain substring``) → the
+plain-form retry (``grep`` with ``{"pattern": "qwen3.8"}``, id
+``call_1``) → the match → the ``read`` of the first match line's
+document (id ``call_2``) → the deterministic echo answer.
+
+KB fixture (TRUNCATE-then-seed, house pattern): ONE source with TWO
+documents of known ``source``/``path``/``title`` (catalog order =
+``(source, path)``, so the first match line is deterministic):
+
+* ``Homelab/llama-server-args.md`` — the CATALOG-FIRST document,
+  indexed WITHOUT chunks (catalog-only; never in the retrieval
+  context, so the flow's ``read`` of it is NOT deduped as
+  already-in-context). It carries the literal line the plain grep
+  finds (``qwen3.8-27b`` — NOT the regex-shaped ``qwen.*3\\.8``,
+  which can never match a fixed-substring grep) and the search-flow
+  sentinel line (the no-regression turn). Its FIRST line is longer
+  than 80 chars, so the mock's first-80-chars quote stays
+  newline-free.
+* ``Homelab/ai-stack-notes.md`` — the retrievable document: one chunk
+  whose embedding is the mock's own bag-of-words vector (the trigger
+  question cosines well past the E2E 0.30 threshold → grounded, the
+  ``<tools>`` section rides along). It carries NO ``qwen3.8`` line
+  (the plain grep's match is the catalog-first document alone) and
+  its name carries no name-hit token (it stays the vector seed only).
+
+Test → phase mapping (Playwright Mapping Rule):
+1. ``test_regex_grep_self_corrects_to_plain_form`` — the grounded
+   GREP-TEACH turn: the turn settles (composer re-enables, ``done``
+   observed), the answer bubble carries the read document's echo
+   (``Read Homelab/llama-server-args.md. <first 80 chars>``), the UI
+   shows the three tool lines (two ``Searching for`` lines + the
+   ``Reading`` line), and no error banner. Wire level: the ``tool``
+   frames arrive in order — ``grep`` ``qwen.*3\\.8`` → ``grep``
+   ``qwen3.8`` → ``read`` the combined identity — and there is NO
+   fourth ``tool`` frame (the loop ended in one correction, not at
+   the round cap).
+2. ``test_plain_search_flow_not_swallowed_by_new_trigger`` — in the
+   SAME session, the GREP-TEACH turn settles and a follow-up question
+   carrying ``SEARCH_TRIGGER`` still settles with the search flow's
+   ``Found …`` answer (the new flow did not swallow the existing
+   trigger).
+"""
+from __future__ import annotations
+
+import hashlib
+import json
+import re
+import time
+from datetime import UTC, datetime
+from pathlib import Path
+
+from playwright.sync_api import Page, expect
+from sqlalchemy import text
+from sqlalchemy.orm import Session
+
+from app.db import SessionLocal
+from app.models import Chunk, Document
+from tests.e2e.mock_llm import (
+    GREP_TEACH_MARKER,
+    GREP_TEACH_PATTERN,
+    GREP_TEACH_PLAIN,
+    GREP_TEACH_TRIGGER,
+    SEARCH_PATTERN,
+    SEARCH_TRIGGER,
+    embed_text,
+)
+
+REPO = Path(__file__).resolve().parents[2]
+
+# --------------------------------------------------------------------------
+# The one-source, two-document fixture (see the module docstring)
+# --------------------------------------------------------------------------
+
+SEED_SOURCE = "Homelab"
+DOC1_PATH = "llama-server-args.md"
+DOC1_TITLE = "Llama Server Args"
+DOC1_SP = f"{SEED_SOURCE}/{DOC1_PATH}"
+
+DOC2_PATH = "ai-stack-notes.md"
+DOC2_TITLE = "AI Stack Notes"
+DOC2_SP = f"{SEED_SOURCE}/{DOC2_PATH}"
+
+#: The catalog-first document (catalog order = (source, path) — DOC1
+#: sorts before DOC2): the plain grep's ONLY match, and the document
+#: the flow reads (so it must NOT be the seed — a seed read dedupes to
+#: "Already in your context.", which the mock flow does not model).
+#: Indexed WITHOUT chunks: catalog-only, never in the retrieval
+#: context. Line 1 (the read quote) is >80 chars and newline-free; it
+#: carries the literal ``qwen3.8-27b`` text (NEVER the regex-shaped
+#: ``qwen.*3\.8`` — that is the whole point of the incident).
+DOC1_CONTENT = (
+    "The llama.cpp server launch line for the qwen3.8-27b juggernaut "
+    "deployment pins the sampling and speculative-decoding flags.\n"
+    "Server command (verbatim): --port 8000 -ctk q8_0 -ctv q8_0 "
+    "--kv-unified -fa on --n-gpu-layers all --jinja.\n"
+    "Model file: /models/qwen3.8-27b/Qwen3.8-27B-UD-Q6_K.gguf with "
+    "the mmproj-BF16.gguf projector and the custom jinja template.\n"
+    f"Regression sentinel line: {SEARCH_PATTERN} must stay findable "
+    "by the plain search flow.\n"
+)
+assert "\n" not in DOC1_CONTENT[:80]  # the read quote stays one line
+assert GREP_TEACH_PLAIN in DOC1_CONTENT  # the plain grep matches DOC1
+assert GREP_TEACH_PATTERN not in DOC1_CONTENT  # the regex never matches
+assert GREP_TEACH_MARKER not in DOC1_CONTENT  # the marker stays tool-side
+
+#: The retrievable document (the grounded seed context): repeated lines
+#: carry the trigger question's key tokens (llama, cpp, arguments,
+#: qwen) — well past the E2E 0.30 cosine threshold — but NO literal
+#: ``qwen3.8`` line (the plain grep's match stays DOC1 alone) and the
+#: name carries no name-hit token (the seed stays the vector side
+#: only). FIRST line >80 chars, newline-free (the seed context stays
+#: one clean line).
+DOC2_CONTENT = (
+    "Notes on the self-hosted ai stack: the llama cpp server arguments "
+    "for every qwen model are kept next to the quadlet files.\n"
+    + (
+        "The llama cpp server arguments — sampling, context, kv cache "
+        "quantization — are documented per model in the quadlet notes.\n"
+    )
+    * 10
+    + "\n## Server notes\n\n"
+    "Every qwen deployment shares the same llama cpp sampling "
+    "defaults; the per-model file overrides the speculative flags.\n"
+)
+assert "\n" not in DOC2_CONTENT[:80]
+assert GREP_TEACH_PLAIN not in DOC2_CONTENT  # the match stays DOC1 alone
+
+#: Carries ``GREP_TEACH_TRIGGER`` (the incident's sample question,
+#: near-verbatim) and nothing else — no other mock marker.
+GREP_TEACH_QUESTION = (
+    "What are the correct llama.cpp arguments for Qwen 3.8? Show me "
+    "the exact server launch line from my notes."
+)
+assert GREP_TEACH_TRIGGER in GREP_TEACH_QUESTION.lower()
+for _other in (
+    "use your tools",
+    "read two documents",
+    "search your documents",
+    "list the files in this directory",
+    "emit raw tool markup",
+    "always emit raw tool markup",
+    "show me a table",
+    "think in paragraphs",
+    "think out loud then hesitate",
+    "think out loud",
+    "show the end of your notes",
+    "write a long answer",
+    "fail then answer",
+    "always fail",
+    "embed fail once",
+    "pretend to think slowly",
+):
+    assert _other not in GREP_TEACH_QUESTION.lower(), _other
+
+#: Carries ``SEARCH_TRIGGER`` (the phase-68 search flow) and nothing
+#: else — the no-regression follow-up question in the same session.
+SEARCH_QUESTION = (
+    "Search your documents for the reese-sentinel-42 marker and tell "
+    "me the line that carries it."
+)
+assert SEARCH_TRIGGER in SEARCH_QUESTION.lower()
+for _other in (
+    GREP_TEACH_TRIGGER,
+    "use your tools",
+    "read two documents",
+    "list the files in this directory",
+    "emit raw tool markup",
+    "always emit raw tool markup",
+    "show me a table",
+    "think in paragraphs",
+    "think out loud then hesitate",
+    "think out loud",
+    "show the end of your notes",
+    "write a long answer",
+    "fail then answer",
+    "always fail",
+    "embed fail once",
+    "pretend to think slowly",
+):
+    assert _other not in SEARCH_QUESTION.lower(), _other
+
+#: The mock's deterministic read echo (the read document reached the
+#: model and landed in the answer) — the flow reads DOC1 (the plain
+#: grep's first — only — match line).
+READ_ANSWER_PREFIX = f"Read {DOC1_SP}."
+READ_ANSWER_QUOTE = DOC1_CONTENT[:80]
+
+
+def _seed_fixture(db: Session) -> None:
+    """The one-source, two-document fixture (see the module docstring).
+
+    DOC1 (catalog-first, the grep match, the read target) is indexed
+    WITHOUT chunks; DOC2 carries the single chunk (the mock's own
+    embedding → the trigger question cosines well past the E2E 0.30
+    threshold → grounded, the ``<tools>`` section rides along).
+    """
+    db.add(
+        Document(
+            source=SEED_SOURCE,
+            path=DOC1_PATH,
+            full_path=f"/tmp/{DOC1_PATH}",
+            title=DOC1_TITLE,
+            content=DOC1_CONTENT,
+            content_hash=hashlib.sha256(DOC1_CONTENT.encode()).hexdigest(),
+            indexed_at=datetime.now(UTC),
+        )
+    )
+    doc2 = Document(
+        source=SEED_SOURCE,
+        path=DOC2_PATH,
+        full_path=f"/tmp/{DOC2_PATH}",
+        title=DOC2_TITLE,
+        content=DOC2_CONTENT,
+        content_hash=hashlib.sha256(DOC2_CONTENT.encode()).hexdigest(),
+        indexed_at=datetime.now(UTC),
+    )
+    db.add(doc2)
+    db.flush()
+    db.add(
+        Chunk(
+            document_id=doc2.id,
+            position=0,
+            content=DOC2_CONTENT,
+            embedding=embed_text(DOC2_CONTENT),
+        )
+    )
+
+
+def _reset_db_fixture() -> None:
+    """Truncate the KB (plus the prompt-shaping tables), then seed the
+    one-source, two-document fixture. ``steering_notes`` /
+    ``kb_overview`` are truncated too, so the HIGH prompt is exactly
+    ``<relevance>`` + ``<documents>`` + ``<tools>`` — byte-stable
+    prompts, byte-stable answers."""
+    with SessionLocal() as db:
+        db.execute(
+            text("TRUNCATE chunks, documents, query_log, steering_notes, kb_overview")
+        )
+        db.commit()
+        _seed_fixture(db)
+        db.commit()
+
+
+# --------------------------------------------------------------------------
+# Page helpers (the house pattern — cf. test_tool_path_teaching.py)
+# --------------------------------------------------------------------------
+
+#: Captures the raw SSE ``data:`` payloads of the /api/chat stream
+#: (a response clone read in the background) — wire-level assertions
+#: for the ``tool`` frames, independent of the UI rendering.
+SSE_HOOK = """
+() => {
+  if (window.__sseInstalled) return;
+  window.__sseInstalled = true;
+  window.__sseFrames = [];
+  const origFetch = window.fetch;
+  window.fetch = async function (...args) {
+    const res = await origFetch.apply(this, args);
+    try {
+      const url = typeof args[0] === 'string' ? args[0] : args[0].url;
+      if (url.includes('/api/chat')) {
+        res.clone().text().then((bodyText) => {
+          for (const block of bodyText.split('\\n\\n')) {
+            const line = block.trim();
+            if (line.startsWith('data: ')) {
+              window.__sseFrames.push(line.slice(6));
+            }
+          }
+        });
+      }
+    } catch (e) { /* non-clonable responses: ignored */ }
+    return res;
+  };
+}
+"""
+
+
+def _install_sse_hook(page: Page) -> None:
+    page.evaluate(SSE_HOOK)
+
+
+def _drain_frames(page: Page) -> list[dict]:
+    """One turn's SSE frames: wait for that turn's ``done`` frame, then
+    return EVERY frame captured since the last drain (the hook's
+    background read appends the whole stream at once after it closes, so
+    clearing-and-reading is race-free per turn)."""
+    deadline = time.monotonic() + 10.0
+    while True:
+        raw = page.evaluate(
+            "() => { const f = window.__sseFrames || []; "
+            "window.__sseFrames = []; return f; }"
+        )
+        parsed = [json.loads(line) for line in raw if line]
+        if any(f.get("type") == "done" for f in parsed):
+            return parsed
+        if time.monotonic() > deadline:
+            raise AssertionError(
+                f"SSE hook captured no `done` frame (frames so far: "
+                f"{len(parsed)}) — hook install failed?"
+            )
+        time.sleep(0.05)
+
+
+def _tool_frames(frames: list[dict]) -> list[dict]:
+    return [f for f in frames if f.get("type") == "tool"]
+
+
+def _submit(page: Page, question: str) -> None:
+    page.fill("#message-input", question)
+    page.click("#send-btn")
+    expect(page.locator(".msg.user .bubble").last).to_contain_text(question)
+
+
+def _wait_settled(page: Page) -> None:
+    """The turn is complete: answer text in the bubble, button recovered.
+
+    Phase 48: the label assertion carries the settle wait with an
+    explicit timeout — the in-flight button is the enabled Stop control
+    (never disabled), so ``to_be_enabled`` no longer blocks until the
+    turn settles."""
+    expect(page.locator(".msg.brain .bubble").last).not_to_have_text("", timeout=30_000)
+    expect(page.locator("#send-btn")).to_be_enabled(timeout=30_000)
+    expect(page.locator("#send-label")).to_have_text("Send", timeout=30_000)
+
+
+def _assert_no_error_banner(page: Page) -> None:
+    """The turn settled through the normal done path — never the red
+    role=alert error banner (the KB-offline banner is a separate,
+    health-driven state the db_ready fixture keeps away)."""
+    banner = page.locator("#kb-banner")
+    expect(banner).to_be_hidden()
+    expect(banner).not_to_have_attribute("role", "alert")
+    expect(banner).not_to_have_class(re.compile(r"is-error"))
+
+
+# --------------------------------------------------------------------------
+# 1. The grounded GREP-TEACH turn: the incident's regex-shaped first
+#    grep → the teaching no-match line → the plain-form retry → the
+#    match → the read → the echo answer — the loop settles in ONE
+#    correction (three tool rounds), pinned on the SSE wire
+# --------------------------------------------------------------------------
+
+
+def test_regex_grep_self_corrects_to_plain_form(
+    page: Page, app_url: str, mock_llm: int, db_ready: None
+) -> None:
+    page.set_default_timeout(30_000)
+    _reset_db_fixture()
+    page.goto(app_url)
+    _install_sse_hook(page)
+
+    _submit(page, GREP_TEACH_QUESTION)
+    _wait_settled(page)
+
+    # Self-correction: the answer quotes the READ document — the plain
+    # grep's match was located, the document reached the model, and the
+    # echo landed in the answer (the wrong-deflection end state — no
+    # tool success, an "I searched everything" refusal — is impossible
+    # on this wire: the done frame below is not deflected).
+    bubble = page.locator(".msg.brain .bubble").last
+    expect(bubble).to_contain_text(READ_ANSWER_PREFIX)
+    expect(bubble).to_contain_text(READ_ANSWER_QUOTE)
+    _assert_no_error_banner(page)
+
+    # The UI shows the three tool lines in order: the regex-shaped
+    # first grep (Searching for <code>qwen.*3\.8</code>), the
+    # plain-form retry (Searching for <code>qwen3.8</code>), the read
+    # of the combined identity.
+    lines = page.locator(".msg.brain .tool-call")
+    expect(lines).to_have_count(3)
+    expect(lines.nth(0)).to_contain_text("Searching for")
+    expect(lines.nth(0).locator("code")).to_have_text(GREP_TEACH_PATTERN)
+    expect(lines.nth(1)).to_contain_text("Searching for")
+    expect(lines.nth(1).locator("code")).to_have_text(GREP_TEACH_PLAIN)
+    expect(lines.nth(2)).to_contain_text("Reading")
+    expect(lines.nth(2).locator("code")).to_have_text(DOC1_SP)
+
+    # Three rounds on the wire: the tool frames arrive in order —
+    # grep qwen.*3\.8 (the incident's regex-shaped first call), grep
+    # qwen3.8 (the plain-form correction the teaching line triggered),
+    # read the combined identity — and there is NO fourth tool frame:
+    # the loop ended in one correction, not at the round cap.
+    frames = _drain_frames(page)
+    assert _tool_frames(frames) == [
+        {"type": "tool", "name": "grep", "argument": GREP_TEACH_PATTERN},
+        {"type": "tool", "name": "grep", "argument": GREP_TEACH_PLAIN},
+        {"type": "tool", "name": "read", "argument": DOC1_SP},
+    ]
+    first_delta = next(i for i, f in enumerate(frames) if f.get("type") == "delta")
+    assert all(
+        i < first_delta for i, f in enumerate(frames) if f.get("type") == "tool"
+    )
+    done = next(f for f in frames if f.get("type") == "done")
+    assert done["deflected"] is False
+    assert not [f for f in frames if f.get("type") == "error"]
+
+
+# --------------------------------------------------------------------------
+# 2. No regression to the plain search flow — the SAME session: after
+#    the GREP-TEACH turn, the SEARCH_TRIGGER follow-up (the phase-68
+#    search flow) still settles with the "Found …" answer
+# --------------------------------------------------------------------------
+
+
+def test_plain_search_flow_not_swallowed_by_new_trigger(
+    page: Page, app_url: str, mock_llm: int, db_ready: None
+) -> None:
+    page.set_default_timeout(30_000)
+    _reset_db_fixture()
+    page.goto(app_url)
+    _install_sse_hook(page)
+
+    # Turn 1 — the GREP-TEACH flow (the incident's regex-shaped first
+    # grep → the teaching line → the plain-form retry → the read → the
+    # echo answer).
+    _submit(page, GREP_TEACH_QUESTION)
+    _wait_settled(page)
+    teach_frames = _drain_frames(page)
+    assert _tool_frames(teach_frames) == [
+        {"type": "tool", "name": "grep", "argument": GREP_TEACH_PATTERN},
+        {"type": "tool", "name": "grep", "argument": GREP_TEACH_PLAIN},
+        {"type": "tool", "name": "read", "argument": DOC1_SP},
+    ]
+    expect(
+        page.locator(".msg.brain .bubble").last
+    ).to_contain_text(READ_ANSWER_PREFIX)
+
+    # Turn 2 — the SAME session: the phase-68 search flow on
+    # SEARCH_TRIGGER. The new flow must not have swallowed the existing
+    # trigger: the follow-up settles with the search flow's answer
+    # (grep the sentinel → "Found <first matched line>").
+    _submit(page, SEARCH_QUESTION)
+    _wait_settled(page)
+
+    second_msg = page.locator(".msg.brain").last
+    lines = second_msg.locator(".tool-call")
+    expect(lines).to_have_count(1)
+    expect(lines.nth(0)).to_contain_text("Searching for")
+    expect(lines.nth(0).locator("code")).to_have_text(SEARCH_PATTERN)
+
+    # The answer is the search flow's echo: "Found <first matched
+    # line's content up to 80 chars>" — the sentinel line from DOC1.
+    sentinel_line = next(
+        line for line in DOC1_CONTENT.splitlines() if SEARCH_PATTERN in line
+    )
+    bubble = second_msg.locator(".bubble").last
+    expect(bubble).to_contain_text(f"Found {sentinel_line[:80]}")
+    _assert_no_error_banner(page)
+
+    # Wire level for the follow-up: one grep of the sentinel pattern —
+    # the search flow, unchanged.
+    frames = _drain_frames(page)
+    assert _tool_frames(frames) == [
+        {"type": "tool", "name": "grep", "argument": SEARCH_PATTERN},
+    ]
+    done = next(f for f in frames if f.get("type") == "done")
+    assert done["deflected"] is False
+    assert not [f for f in frames if f.get("type") == "error"]

tests/integration/test_name_hit_lexical.py

@@ -0,0 +1,207 @@
+"""Integration: the name-hit lexical signal against real Postgres (the
+2026-09-05 "Qwen 3.8" incident).
+
+The unit suite (``tests/unit/test_retriever.py``) covers the pure
+mapping with fake rows; this suite covers the SQL side on real
+Postgres: the document-projection scan, the LATERAL representative-
+chunk fetch (the ``is_summary`` chunk wins, chunk 0 otherwise, and a
+chunk-less name match is EXCLUDED — the ``c.id IS NOT NULL`` guard),
+the (count, length, catalog) ranking, the name-hits-lead-the-lexical-
+list union with the FTS rows (chunk-id dedup), and the full
+``retrieve()`` → ``select_documents()`` path putting the versioned-
+name document into the seeded top-N.
+
+Requires: ``podman compose up -d db``.
+"""
+from __future__ import annotations
+
+import uuid
+from collections.abc import Iterator
+from datetime import UTC, datetime
+
+import pytest
+from sqlalchemy import text
+from sqlalchemy.orm import Session
+
+from app.models import Chunk, Document
+from app.rag.retriever import (
+    NAME_HIT_LIMIT,
+    _lexical_candidates,
+    _name_hit_chunks,
+    retrieve,
+    select_documents,
+)
+
+INCIDENT_QUESTION = "What are the correct llama.cpp arguments for Qwen 3.8?"
+
+#: 768-dim test vectors (the pgvector column's dimension) — axis unit
+#: vectors so the cosines are exact (1.0 parallel, 0.0 orthogonal,
+#: 0.7071 half-parallel).
+D = 768
+
+
+def _vec(axis: int, second: bool = False) -> list[float]:
+    v = [0.0] * D
+    v[axis] = 1.0
+    if second:
+        v[axis + 1] = 1.0
+    return v
+
+
+def _doc(db: Session, source: str, path: str, title: str, content: str) -> Document:
+    doc = Document(
+        id=uuid.uuid4(),
+        source=source,
+        path=path,
+        full_path=f"/tmp/{source}/{path}",
+        title=title,
+        content=content,
+        content_hash="0" * 64,
+        indexed_at=datetime.now(UTC),
+    )
+    db.add(doc)
+    return doc
+
+
+def _chunk(
+    db: Session, doc: Document, position: int, content: str, is_summary: bool = False
+) -> Chunk:
+    chunk = Chunk(
+        id=uuid.uuid4(),
+        document_id=doc.id,
+        position=position,
+        content=content,
+        is_summary=is_summary,
+    )
+    db.add(chunk)
+    return chunk
+
+
+@pytest.fixture()
+def kb(db) -> Iterator[None]:
+    """A fresh KB with the incident shape: the qwen3.8 quadlet (the
+    name hit, with a summary chunk + an ordinary chunk), a qwen3.6
+    quadlet (same family, different version — NOT a hit), an
+    unrelated document (FTS-only candidate), and a chunk-less document
+    whose name DOES carry the token (the exclusion guard)."""
+    db.execute(text("TRUNCATE chunks, documents"))
+    db.commit()
+
+    q38 = _doc(
+        db,
+        "deploy",
+        "reeseapps/ai/deployments/juggernaut/quadlets/qwen3.8-27b-juggernaut-vulkan.container",
+        "qwen3.8-27b-juggernaut-vulkan",
+        "# llama.cpp juggernaut\nExec=--port 8000 -ctk q8_0 -ctv q8_0 --jinja\n"
+        "-m /models/qwen3.8-27b/Qwen3.8-27B-UD-Q6_K.gguf\n",
+    )
+    _chunk(
+        db,
+        q38,
+        -1,
+        "Podman quadlet: llama.cpp server for Qwen 3.8 27B (juggernaut).",
+        is_summary=True,
+    )
+    _chunk(db, q38, 0, "# llama.cpp juggernaut\nExec=--port 8000 -ctk q8_0")
+    db.flush()
+    # A vector the question vector (below) cosines with — non-NULL so
+    # the chunk is eligible for the vector list too.
+    for c in q38.chunks:
+        c.embedding = _vec(1)
+    db.commit()
+
+    q36 = _doc(
+        db,
+        "deploy",
+        "reeseapps/ai/deployments/juggernaut/quadlets/qwen3.6-27b-juggernaut-vulkan.container",
+        "qwen3.6-27b-juggernaut-vulkan",
+        "# llama.cpp juggernaut\n-m /models/qwen3.6-27b/model.gguf\n",
+    )
+    c36 = _chunk(db, q36, 0, "# llama.cpp juggernaut\n-m /models/qwen3.6-27b/model.gguf")
+    c36.embedding = _vec(0)  # orthogonal to the question vector
+    db.commit()
+
+    other = _doc(
+        db, "homelab", "notes/llama.cpp.md", "llama.cpp notes", "llama cpp server arguments notes\n"
+    )
+    c_other = _chunk(db, other, 0, "llama cpp server arguments notes")
+    c_other.embedding = _vec(1, second=True)  # half-parallel to the question
+    db.commit()
+
+    # Name carries the token, ZERO chunks — the exclusion guard.
+    _doc(db, "deploy", "qwen3.8-empty.container", "qwen3.8-empty", "(empty file)")
+    db.commit()
+    yield
+    db.execute(text("TRUNCATE chunks, documents"))
+    db.commit()
+
+
+def test_name_hit_chunks_real_sql(kb, db) -> None:
+    """Real Postgres: the projection scan finds exactly the qwen3.8
+    quadlet (the qwen3.6 sibling and the chunk-less name match are
+    excluded), and the LATERAL fetch hands back the SUMMARY chunk as
+    the representative (position −1, is_summary)."""
+    out = _name_hit_chunks(db, INCIDENT_QUESTION)
+    assert [rc.document.path for rc in out] == [
+        "reeseapps/ai/deployments/juggernaut/quadlets/qwen3.8-27b-juggernaut-vulkan.container"
+    ]
+    rc = out[0]
+    assert rc.position == -1  # the summary chunk wins the LATERAL order
+    assert rc.is_summary is True
+    assert rc.fts_hit is True  # the lexical signal — the A8 gate answers
+    assert rc.cosine == 0.0  # no vector rank on the name-hit row
+    assert "qwen3.8-empty.container" not in [r.document.path for r in out]  # chunk-less guard
+
+
+def test_lexical_candidates_name_hit_leads_real_sql(kb, db) -> None:
+    """The full lexical list on real Postgres: the name hit leads, the
+    FTS rows follow (the qwen3.6 and llama.cpp docs both match the
+    OR-tsquery on llama|cpp|arguments|… — the pre-incident pollution —
+    but the name hit still ranks them behind it)."""
+    out = _lexical_candidates(db, INCIDENT_QUESTION, limit=30)
+    paths = [rc.document.path for rc in out]
+    assert paths[0] == (
+        "reeseapps/ai/deployments/juggernaut/quadlets/qwen3.8-27b-juggernaut-vulkan.container"
+    )
+    # The FTS pollution is still present (the incident's shape) — but
+    # behind the name hit, no longer ahead of it.
+    assert (
+        "reeseapps/ai/deployments/juggernaut/quadlets/qwen3.6-27b-juggernaut-vulkan.container"
+        in paths
+    )
+    assert all(rc.fts_hit is True for rc in out)
+
+
+def test_retrieve_selects_name_hit_doc_into_top_n(kb, db) -> None:
+    """The product path: hybrid ``retrieve()`` (vector ∪ lexical, RRF
+    fused) → ``select_documents`` puts the qwen3.8 quadlet in the
+    seeded top-N — the incident's seed miss (the two overview docs
+    only) is fixed. The question vector is parallel to the q38 chunk
+    embeddings (cosine 1.0), orthogonal to q36 (0.0)."""
+    question_vec = _vec(1)
+    chunks = retrieve(db, INCIDENT_QUESTION, question_vec)
+    docs = select_documents(chunks, n=2)
+    assert [d.path for d in docs] == [
+        "reeseapps/ai/deployments/juggernaut/quadlets/qwen3.8-27b-juggernaut-vulkan.container",
+        "notes/llama.cpp.md",
+    ]
+
+
+def test_name_hit_limit_real_sql(db) -> None:
+    """Twelve identical (1, 6) name hits — the LATERAL fetch (and the
+    output) carries exactly ``NAME_HIT_LIMIT`` winners, catalog order."""
+    db.execute(text("TRUNCATE chunks, documents"))
+    db.commit()
+    for i in range(12):
+        doc = _doc(
+            db, "S", f"quadlets/m{i:02d}-qwen38.container", f"m{i:02d}-qwen38", "llama cpp qwen38\n"
+        )
+        db.flush()
+        c = _chunk(db, doc, 0, f"llama cpp qwen38 doc {i}")
+        c.embedding = _vec(2)
+    db.commit()
+    out = _name_hit_chunks(db, "what are the llama.cpp arguments for qwen 3.8")
+    assert len(out) == NAME_HIT_LIMIT
+    assert [rc.document.path for rc in out] == [
+        f"quadlets/m{i:02d}-qwen38.container" for i in range(NAME_HIT_LIMIT)
+    ]

tests/unit/test_agent.py

@@ -209,17 +209,26 @@ def test_agent_tools_names_and_parameters() -> None:
     # ("pass ONLY `pattern`") + the source-name-is-not-a-document
     # clause (the model kept scoping grep with an ls-style source name
     # — the 2026-09-03 incident loop shape, but on grep) plus the
-    # one-call-at-a-time discipline clause.
+    # one-call-at-a-time discipline clause. The 2026-09-05 incident
+    # (the "Qwen 3.8" sample question — the harness prior is that grep
+    # takes a REGEX; this grep is a fixed substring, owner-locked A5):
+    # the plain-substring-never-a-regex clause states the contract up
+    # front, so the regex-shaped first grep that does fire gets the
+    # teaching no-match line instead of a trusted miss.
     assert grep["description"] == (
         "Search the indexed documents for an exact string "
         "(case-insensitive) and return up to 20 matching lines "
         "as `source/path:line: text` — a locator, not a "
-        "context-adder: read the winner with `read`. For a "
+        "context-adder: read the winner with `read`. The "
-        "normal search pass ONLY `pattern` — it searches every "
+        "pattern is a plain substring, NEVER a regex — if a "
-        "document and that is how you search the knowledge "
+        "pattern with regex syntax (like '.*' or '\\.') comes "
-        "base; never pass a source name as `path` (a source "
+        "back with no matches, retry with the plain text you "
-        "name is not a document). Call one tool at a time — "
+        "expect to see. For a normal search pass ONLY `pattern` "
-        "wait for this result before your next call."
+        "— it searches every document and that is how you "
+        "search the knowledge base; never pass a source name "
+        "as `path` (a source name is not a document). Call one "
+        "tool at a time — wait for this result before your "
+        "next call."
     )
     grep_params = grep["parameters"]
     assert grep_params["type"] == "object"
@@ -227,7 +236,8 @@ def test_agent_tools_names_and_parameters() -> None:
     assert set(grep_params["properties"]) == {"pattern", "path"}
     assert all(p["type"] == "string" for p in grep_params["properties"].values())
     assert grep_params["properties"]["pattern"]["description"] == (
-        "The exact text to search for (a plain substring, not a regex)"
+        "The exact text to search for (a plain substring, "
+        "not a regex — no '.*', no '\\.', no character classes)"
     )
     # Phase 72 (task 02): the bare-path contract is stated up front;
     # task 05 (live gate iterations 1-8): the one-known-document clause
@@ -1164,6 +1174,184 @@ def test_grep_truncates_match_lines_at_200_chars(monkeypatch: pytest.MonkeyPatch
     assert holder.tool_calls == 1
 
 
+# ---------- grep no-match teaching: the regex-shaped pattern
+# (the 2026-09-05 "Qwen 3.8" incident — the harness prior is that
+# grep takes a REGEX; this grep is a fixed substring, owner-locked
+# A5, and the contract does not change) ----------
+
+
+def test_plain_form_reduces_regex_to_literal_text() -> None:
+    """The plain-form hint: the pattern reduced to literal text — the
+    incident's exact recovery (``qwen.*3\\.8`` → ``qwen3.8``) plus the
+    edge cases (raw ``.*`` runs dropped before unescape, so an escaped
+    dot survives; first alternative only; classes/quantifiers/parens/
+    anchors gone; whitespace preserved; pure metacharacters → ``""``).
+    """
+    assert agent.plain_form(r"qwen.*3\.8") == "qwen3.8"  # the incident
+    assert agent.plain_form(r"qwen 3\.8") == "qwen 3.8"
+    assert agent.plain_form(r"Qwen 3\.8") == "Qwen 3.8"  # case kept
+    assert agent.plain_form(r"qwen3\.8") == "qwen3.8"
+    assert agent.plain_form(r"llama\.cpp") == "llama.cpp"  # escaped dot kept
+    assert agent.plain_form(r"qwen[0-9]+") == "qwen"  # class + quantifier
+    assert agent.plain_form("a|b") == "a"  # first alternative only
+    assert agent.plain_form(r"\d+") == ""  # no literal text — no hint
+    assert agent.plain_form(r".*") == ""  # pure wildcard — no hint
+    assert agent.plain_form(r"(qwen)3\.8") == "qwen3.8"  # group contents kept
+    assert agent.plain_form("a{2,3}b") == "ab"
+    assert agent.plain_form(r"^qwen$") == "qwen"  # anchors dropped
+    assert agent.plain_form(r"a\.b") == "a.b"  # escaped dot is a literal
+    assert agent.plain_form("plain") == "plain"  # identity for plain text
+
+
+def test_looks_like_regex_detection() -> None:
+    """One metacharacter anywhere marks the pattern regex-shaped; a
+    plain substring (even with a space) does not."""
+    for p in (
+        r"qwen.*3\.8", r"qwen 3\.8", "qwen+", "a?b", "x|y", "(a)", "[a-z]", "a^b", "b$c", "a{2}"
+    ):
+        assert agent.looks_like_regex(p) is True, p
+    for p in ("qwen 3.8", "qwen3.8", "plain substring", ""):
+        assert agent.looks_like_regex(p) is False, p
+
+
+def test_grep_no_match_regex_pattern_gets_teaching_line(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The incident's shape: a regex-shaped pattern that (necessarily)
+    misses gets the TEACHING no-match line — the plain-substring
+    contract stated, the plain-form retry hint handed over. Still a
+    counted result; the context is untouched (locked A5)."""
+    d1 = _doc("Alpha", "a/one.md", "One", "qwen3.8-27b juggernaut\nno regex text")
+    monkeypatch.setattr(agent, "all_documents", lambda db: [d1])
+    holder = AgentHolder()
+    llm = ScriptedLLM(
+        [
+            ToolCallPiece(
+                id="call_1", name="grep", arguments={"pattern": r"qwen.*3\.8"}
+            )
+        ],
+        [StreamPiece("content", "ans")],
+    )
+    asyncio.run(_run(llm, holder, _settings()))
+    assert llm.requests[1][0][3]["content"] == agent.NO_MATCHES_REGEX.format(
+        pattern=r"qwen.*3\.8", plain="qwen3.8"
+    )
+    assert llm.requests[1][0][3]["content"] == (
+        "No matches for 'qwen.*3\\.8'. grep matches a plain substring "
+        "(case-insensitive), not a regex — '.*', '\\.' and the like are "
+        "literal text here, so that pattern can never match. Retry with "
+        "the plain text you expect to see (e.g. 'qwen3.8')."
+    )
+    assert holder.tool_calls == 1  # a no-match with teaching is still a result
+    assert holder.read_docs == []  # locked A5: a grep adds no context
+
+
+def test_grep_no_match_regex_scoped_gets_teaching_line(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The scoped teaching variant: the resolved identity is echoed, the
+    hint handed over."""
+    d1 = _doc("Alpha", "a/one.md", "One", "nothing regex-shaped here")
+
+    def _find(db: Any, source: str, path: str) -> Document | None:
+        return d1 if (source, path) == ("Alpha", "a/one.md") else None
+
+    monkeypatch.setattr(agent, "find_document", _find)
+    holder = AgentHolder()
+    llm = ScriptedLLM(
+        [
+            ToolCallPiece(
+                id="call_1",
+                name="grep",
+                arguments={"pattern": r"qwen 3\.8", "path": "Alpha/a/one.md"},
+            )
+        ],
+        [StreamPiece("content", "ans")],
+    )
+    asyncio.run(_run(llm, holder, _settings()))
+    assert llm.requests[1][0][3]["content"] == (
+        "No matches for 'qwen 3\\.8' in Alpha/a/one.md. grep matches a "
+        "plain substring (case-insensitive), not a regex — retry with "
+        "the plain text you expect to see (e.g. 'qwen 3.8')."
+    )
+    assert holder.tool_calls == 1
+    assert holder.read_docs == []
+
+
+def test_grep_no_match_plain_pattern_keeps_ordinary_line(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A no-match for a PLAIN pattern (no metacharacters — "qwen 3.8" with
+    the space included) keeps the ordinary line byte-identical: the
+    teaching never fires for a well-formed pattern (the retrieval side —
+    the name-hit lexical signal — is what covers that case)."""
+    d1 = _doc("Alpha", "a/one.md", "One", "qwen3.8-27b juggernaut")
+    monkeypatch.setattr(agent, "all_documents", lambda db: [d1])
+    holder = AgentHolder()
+    llm = ScriptedLLM(
+        [ToolCallPiece(id="call_1", name="grep", arguments={"pattern": "qwen 3.8"})],
+        [StreamPiece("content", "ans")],
+    )
+    asyncio.run(_run(llm, holder, _settings()))
+    assert llm.requests[1][0][3]["content"] == (
+        "No matches for 'qwen 3.8' in the knowledge base."
+    )
+    assert holder.tool_calls == 1
+
+
+def test_grep_matched_regex_pattern_returns_matches_not_teaching(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A pattern with metacharacters that MATCHES literally gets the
+    ordinary match output — the teaching can never suppress a real hit
+    (the detection keys on a NO-MATCH only)."""
+    d1 = _doc("S", "a.md", "A", "the C++ compiler is here")
+    monkeypatch.setattr(agent, "all_documents", lambda db: [d1])
+    holder = AgentHolder()
+    llm = ScriptedLLM(
+        [ToolCallPiece(id="call_1", name="grep", arguments={"pattern": "C++"})],
+        [StreamPiece("content", "ans")],
+    )
+    asyncio.run(_run(llm, holder, _settings()))
+    assert llm.requests[1][0][3]["content"] == "S/a.md:1: the C++ compiler is here"
+    assert holder.tool_calls == 1
+
+
+def test_grep_no_match_regex_reducing_to_empty_falls_back(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A regex-shaped pattern with no literal text left after the
+    reduction (``.*``) gets the ORDINARY line — no empty hint."""
+    d1 = _doc("Alpha", "a/one.md", "One", "any text at all")
+    monkeypatch.setattr(agent, "all_documents", lambda db: [d1])
+    holder = AgentHolder()
+    llm = ScriptedLLM(
+        [ToolCallPiece(id="call_1", name="grep", arguments={"pattern": r".*"})],
+        [StreamPiece("content", "ans")],
+    )
+    asyncio.run(_run(llm, holder, _settings()))
+    assert llm.requests[1][0][3]["content"] == (
+        "No matches for '.*' in the knowledge base."
+    )
+    assert holder.tool_calls == 1
+
+
+def test_no_matches_regex_templates_pin() -> None:
+    """The teaching templates are verbatim pins (the model-facing copy —
+    the mock E2E keys off the plain-substring clause)."""
+    assert agent.NO_MATCHES_REGEX == (
+        "No matches for '{pattern}'. grep matches a plain substring "
+        "(case-insensitive), not a regex — '.*', '\\.' and the like are "
+        "literal text here, so that pattern can never match. Retry with "
+        "the plain text you expect to see (e.g. '{plain}')."
+    )
+    assert agent.NO_MATCHES_REGEX_SCOPED == (
+        "No matches for '{pattern}' in {source}/{path}. grep matches a "
+        "plain substring (case-insensitive), not a regex — retry with "
+        "the plain text you expect to see (e.g. '{plain}')."
+    )
+
+
 def test_grep_scoped_to_one_document(monkeypatch: pytest.MonkeyPatch) -> None:
     """Scoped grep: only the named document is loaded (find_document on
     the first-slash split), ``all_documents`` never runs, and the match

tests/unit/test_retriever.py

@@ -133,6 +133,20 @@ def test_lexical_tsquery_stopwords_left_to_postgres() -> None:
     assert lexical_tsquery("how do i") == "how | do | i"
 
 
+def test_lexical_tsquery_dotted_tokens_kept_whole() -> None:
+    """The 2026-09-05 incident: the default parser lexes dotted words
+    as ONE lexeme ("llama.cpp" → 'llama.cpp', "Qwen 3.8" → '3.8'), so
+    the query carries them whole — split tokens (llama | cpp) can never
+    match the document side."""
+    assert lexical_tsquery(
+        "What are the correct llama.cpp arguments for Qwen 3.8?"
+    ) == "what | are | the | correct | llama.cpp | arguments | for | qwen | 3.8"
+    # The dash still splits (only dots group): ai | internal.network.
+    assert lexical_tsquery("how did I set up ai-internal.network?") == (
+        "how | did | i | set | up | ai | internal.network"
+    )
+
+
 def test_fuse_combines_both_lists_for_double_hits() -> None:
     v1 = _rc("a.md", cosine=0.9)
     v2 = _rc("b.md", cosine=0.5)
@@ -196,7 +210,14 @@ def test_fuse_empty_lists() -> None:
 # ---------------------------------------------------------------------------
 
 from app.models import Chunk  # noqa: E402
-from app.rag.retriever import _lexical_candidates, _vector_candidates  # noqa: E402
+from app.rag.retriever import (  # noqa: E402
+    NAME_HIT_LIMIT,
+    _lexical_candidates,
+    _name_hit_chunks,
+    _normalize_name,
+    _vector_candidates,
+    name_hit_tokens,
+)
 
 
 class _FakeResult:
@@ -210,15 +231,29 @@ class _FakeResult:
 
 
 class _FakeSession:
-    """Returns canned rows from ``execute`` without touching Postgres."""
+    """Returns canned rows from ``execute`` without touching Postgres.
 
-    def __init__(self, rows: list) -> None:
+    One list of rows (legacy form) is returned for EVERY call; several
-        self._rows = rows
+    lists (one per successive ``execute``) model a query sequence — the
+    name-hit lexical path (2026-09-05) issues the document-projection
+    query and, when hits exist, the LATERAL chunk query, BEFORE the FTS
+    query.
+    """
+
+    def __init__(self, *rowsets: list) -> None:
+        if len(rowsets) == 1 and not (
+            rowsets[0] and isinstance(rowsets[0][0], list)
+        ):
+            rowsets = (rowsets[0],)  # the single-rowset legacy form
+        self._rowsets = rowsets
+        self._call = 0
         self.statements: list = []
 
     def execute(self, stmt, params: dict | None = None) -> _FakeResult:
         self.statements.append((stmt, params))
-        return _FakeResult(self._rows)
+        rows = self._rowsets[min(self._call, len(self._rowsets) - 1)]
+        self._call += 1
+        return _FakeResult(rows)
 
 
 def _chunk_row(is_summary: bool) -> Chunk:
@@ -286,9 +321,17 @@ def _lexical_row(is_summary: bool, doc_path: str) -> object:
 
 
 def test_lexical_candidates_carry_is_summary_flag() -> None:
-    """The lexical list reads ``c.is_summary`` from the raw row."""
+    """The lexical list reads ``c.is_summary`` from the raw row.
+
+    The question carries no digit-bearing name token (no bare, no
+    numeric-join), so the name-hit path issues NO queries at all — the
+    single FTS rowset answers the only (FTS) call, and the list is the
+    plain FTS rows: the pre-name-hit behavior, unchanged.
+    """
     rows = [_lexical_row(True, "summary-src.yaml"), _lexical_row(False, "other.md")]
-    out = _lexical_candidates(_FakeSession(rows), "how do i configure the thing", limit=10)  # pyright: ignore[reportArgumentType]
+    out = _lexical_candidates(
+        _FakeSession(rows), "how do i configure the thing", limit=10  # pyright: ignore[reportArgumentType]
+    )
     assert len(out) == 2
     by_path = {rc.document.path: rc for rc in out}
     assert by_path["summary-src.yaml"].is_summary is True
@@ -323,3 +366,180 @@ def test_fuse_default_is_summary_stays_false_for_legacy_chunks() -> None:
     out = fuse([_rc("a.md", cosine=0.8)], [_rc("b.md")], k=60)
     assert len(out) == 2
     assert all(rc.is_summary is False for rc in out)
+
+
+# ---------------------------------------------------------------------------
+# Name-hit lexical signal (the 2026-09-05 incident — the versioned-name
+# case the default parser lexes incompatibly: "Qwen 3.8" → qwen/3/8 can
+# never match a document's qwen3/8/27b tokens)
+# ---------------------------------------------------------------------------
+
+INCIDENT_QUESTION = "What are the correct llama.cpp arguments for Qwen 3.8?"
+
+
+def test_normalize_name() -> None:
+    assert _normalize_name("Qwen 3.8") == "qwen38"
+    assert _normalize_name("qwen3.8-27b-juggernaut-vulkan") == "qwen3827bjuggernautvulkan"
+    assert _normalize_name("Mixed CASE-99") == "mixedcase99"
+    assert _normalize_name("!!!") == ""
+
+
+def test_name_hit_tokens_incident_question() -> None:
+    """The incident question yields EXACTLY the versioned join
+    ``qwen38`` — the token the document names actually carry. Plain
+    prose words (``what``, ``llamacpp``, ``arguments``, ``server`` —
+    no digit) never name-match (the precision guard); the single
+    digits ("3", "8") and the bare "38" are < 4 chars; the
+    digit-leading ``38show`` boundary artifact is dropped."""
+    tokens = name_hit_tokens(INCIDENT_QUESTION)
+    assert tokens == ["qwen38"]
+    for absent in ("what", "qwen", "llamacpp", "arguments", "3", "8", "38", "38show", "server"):
+        assert absent not in tokens
+
+
+def test_name_hit_tokens_no_digit_question_returns_empty() -> None:
+    """A question with no digit-bearing token (bare or joined) yields
+    no name candidates — prose joins like ``correctllama`` never count."""
+    assert name_hit_tokens("what is the correct caddy config") == []
+    assert name_hit_tokens("a e i o u 3 8") == []
+
+
+def test_name_hit_tokens_bare_digit_bearing_token() -> None:
+    """A single written token that carries a digit (``1panel``) is a
+    name candidate on its own — no join needed."""
+    tokens = name_hit_tokens("what is my 1panel dashboard setup")
+    assert tokens == ["1panel"]
+
+
+def _name_row(doc: Document) -> tuple:
+    """One row of the name-hit document projection (catalog order)."""
+    return (doc.id, doc.source, doc.path, doc.title)
+
+
+def _name_hit_lateral_row(doc: Document, is_summary: bool = False) -> SimpleNamespace:
+    """One row of the name-hit LATERAL chunk query."""
+    return SimpleNamespace(
+        doc_id=doc.id,
+        source=doc.source,
+        path=doc.path,
+        full_path=doc.full_path,
+        title=doc.title,
+        doc_content=doc.content,
+        content_hash=doc.content_hash,
+        indexed_at=None,
+        chunk_id=uuid.uuid4(),
+        position=-1 if is_summary else 0,
+        content="summary chunk" if is_summary else "content chunk",
+        is_summary=is_summary,
+    )
+
+
+def test_name_hit_chunks_no_tokens_skips_all_queries() -> None:
+    """A question with no name tokens issues no queries at all."""
+    session = _FakeSession([])  # any call would surface a statement
+    assert _name_hit_chunks(session, "a e i o u 3 8") == []  # pyright: ignore[reportArgumentType]
+    assert session.statements == []
+
+
+def test_name_hit_chunks_no_matching_doc_returns_empty() -> None:
+    """Name tokens exist but no document name carries one: the
+    projection runs, the LATERAL fetch does not."""
+    doc = _doc("quadlets/other.container", "body")
+    name_rows = [_name_row(doc)]
+    session = _FakeSession(name_rows, [])
+    assert _name_hit_chunks(session, INCIDENT_QUESTION) == []  # pyright: ignore[reportArgumentType]
+    assert len(session.statements) == 1  # projection only — no LATERAL fetch
+
+
+def test_name_hit_chunks_ranked_by_count_length_catalog() -> None:
+    """A two-candidate question (``qwen38`` + ``1panel``): the document
+    whose name carries BOTH (2 matches, 12 total chars) leads; the two
+    single-match documents tie on (1, 6) and fall to catalog order
+    (``dashboards/1panel-notes.md`` before ``quadlets/qwen3.8…``).
+    Hits carry ``fts_hit=True`` (the A8 gate answers), ``cosine=0.0``,
+    and the summary flag of their representative chunk."""
+    both = _doc("dashboards/1panel-qwen3.8.md", "body", title="1Panel Qwen 3.8")
+    panel = _doc("dashboards/1panel-notes.md", "body")
+    q38 = _doc("quadlets/qwen3.8-27b-juggernaut-vulkan.container", "body")
+    name_rows = [_name_row(d) for d in (panel, both, q38)]  # catalog order
+    question = "what are the correct llama.cpp arguments for qwen 3.8 and the 1panel dashboard?"
+    lateral_rows = [
+        _name_hit_lateral_row(q38, is_summary=True),  # LATERAL may return any order
+        _name_hit_lateral_row(both),
+        _name_hit_lateral_row(panel),
+    ]
+    session = _FakeSession(name_rows, lateral_rows)
+    out = _name_hit_chunks(session, question)  # pyright: ignore[reportArgumentType]
+    assert [rc.document.path for rc in out] == [
+        "dashboards/1panel-qwen3.8.md",  # 2 matched tokens — leads
+        "dashboards/1panel-notes.md",  # (1, 6) — catalog order
+        "quadlets/qwen3.8-27b-juggernaut-vulkan.container",  # (1, 6) — after
+    ]
+    assert all(rc.fts_hit is True for rc in out)  # the lexical signal
+    assert all(rc.cosine == 0.0 for rc in out)  # no vector rank
+    assert all(rc.score == 0.0 for rc in out)  # fuse fills the score
+    by_path = {rc.document.path: rc for rc in out}
+    assert by_path["quadlets/qwen3.8-27b-juggernaut-vulkan.container"].is_summary is True
+    assert by_path["quadlets/qwen3.8-27b-juggernaut-vulkan.container"].position == -1
+    assert by_path["dashboards/1panel-notes.md"].is_summary is False
+
+
+def test_name_hit_chunks_capped_at_limit() -> None:
+    """Twelve tied name hits (one matched token each) yield exactly
+    ``NAME_HIT_LIMIT`` of them — catalog order (the deterministic
+    tie-break)."""
+    docs = [_doc(f"quadlets/m{i:02d}.container", "body") for i in range(12)]
+    for d in docs:  # give every document a name that carries the token
+        d.title = "qwen38 model i"
+    name_rows = [_name_row(d) for d in docs]
+    # Only the ten winners (catalog order — the deterministic tie-break
+    # of the twelve identical scores) reach the LATERAL fetch; the fake
+    # answers with exactly those rows.
+    lateral_rows = [_name_hit_lateral_row(d) for d in docs[:NAME_HIT_LIMIT]]
+    session = _FakeSession(name_rows, lateral_rows)
+    out = _name_hit_chunks(
+        session, "tell me about the qwen 3.8 models"  # pyright: ignore[reportArgumentType]
+    )
+    assert len(out) == NAME_HIT_LIMIT
+    assert [rc.document.path for rc in out] == [f"quadlets/m{i:02d}.container" for i in range(10)]
+
+
+def test_lexical_candidates_name_hits_lead_and_dedupe_with_fts() -> None:
+    """The full lexical list: name hits LEAD (their representative
+    chunks), the FTS rows follow, and an FTS row sharing the name hit's
+    chunk id appears exactly once (deduped)."""
+    q38 = _doc("quadlets/qwen3.8-27b-juggernaut-vulkan.container", "body")
+    other = _doc("quadlets/qwen38-other.container", "body")  # 1 matched token
+    name_rows = [_name_row(q38), _name_row(other)]
+    q38_chunk = uuid.uuid4()
+
+    def _lateral(doc: Document) -> SimpleNamespace:
+        row = _name_hit_lateral_row(doc)
+        if doc is q38:
+            row.chunk_id = q38_chunk
+        return row
+
+    lateral_rows = [_lateral(q38), _lateral(other)]
+    fts_rows = [
+        # an FTS hit on the SAME chunk as the q38 name hit (deduped away)
+        SimpleNamespace(
+            chunk_id=q38_chunk, position=1, content="c", doc_id=q38.id,
+            source=q38.source, path=q38.path, full_path=q38.full_path,
+            title=q38.title, doc_content=q38.content, content_hash=q38.content_hash,
+            indexed_at=None, is_summary=False, rank=0.1,
+        ),
+        # an FTS hit on a different chunk of the OTHER doc (kept)
+        _lexical_row(False, "quadlets/qwen38-other.container"),
+    ]
+    session = _FakeSession(name_rows, lateral_rows, fts_rows)
+    out = _lexical_candidates(session, INCIDENT_QUESTION, limit=10)  # pyright: ignore[reportArgumentType]
+    assert len(out) == 3  # q38 (once), other (name hit), other (FTS chunk)
+    # Both name hits tie on (1, 6) — catalog order: "qwen3." (ASCII 46)
+    # sorts before "qwen38" (ASCII 56).
+    assert out[0].document.path == "quadlets/qwen3.8-27b-juggernaut-vulkan.container"
+    assert out[1].document.path == "quadlets/qwen38-other.container"
+    assert out[0].chunk_id == q38_chunk  # the name-hit representative row
+    assert {
+        rc.chunk_id for rc in out
+    } == {q38_chunk, fts_rows[1].chunk_id, lateral_rows[1].chunk_id}
+    assert all(rc.fts_hit is True for rc in out)